DESCRIPTION: (from applicant's abstract): The serotonin alpha (5-HTIalpha) receptor system plays a central role in the control of serotonergic neurotransmission and, as such, features prominently in many behaviors and physiological functions. In addition. the regulation of this receptor and its effector mechanisms has been the focus of intense interest because of their importance in the therapeutic action of anxiolytic and antidepressant drugs. For example, numerous basic and clinical investigations are being carried out to test the theory that a progressive decrease in the responsiveness (desensitization) of 5-HT1alpha autoreceptors is necessary for the therapeutic effectiveness in depression of selective serotonin reuptake inhibitors (SSRIs). Although we have learned a considerable amount about the cellular signal transduction pathways coupled to the 5-HT1alpha receptor, we know very little about how the function of this important receptor system is regulated. An understanding of cellular factors that regulate 5-HT1alpha receptor signaling may provide insight into the etiology of affective disorders, help us to understand the mechansism of action of drugs such as SSRIs, and possibly aid in the development of new drugs and/or therapeutic strategies. Our goal is to study regulation of the responsiveness of the 5-HT1alpha receptor system by activation of two major cellular signaling cascades (phospholipases C {PLC} and alpha2 {PLalpha2}). Experiments with clonal cell lines are designed to delineate the mechanisms by which the PLC and PLA2 signaling cascades regulate 5-HT1alpha receptor system responsiveness. Through the use of selective inhibitors, antisense strategies, receptor phosphorylation and site-directed mutagenesis studies, we will identify the components of the PLC and Plalpha2 signaling cascades that differentially regulate 5-HT1alpha receptor function and determine if the 5-HTIA receptor itself is the target for their actions. The generation of stable cell lines that express cloned G-protein-gated inward rectifier channels (GIRKs) will permit regulation of both responses coupled to the 5-HT1alpha receptor (inhibition of adenylyl cyclase and increase in K+ conductance) to be studied in the same cells. The physiological relevance of effects elicted by activation of phospholipase signaling cascades will be probed with experiments using rat brain slices containing the dorsal raphe nucleus and hippocampus as models for pre-and postsynaptic 5-HT I A receptors, respectively. Components of the phospholipase cascades responsible for changes in functon will be identified using intracellular deliverv of selective inhibitors with whole cell recording techniques. The integration of brain slice preparations and clonal cell systems Will pernift rigorous study of the regulation of 5-HTI A receptor function.